Question: As the swim coach at Covington, Emily selects which athletes will participate in the state-wide swim relay. The relay team swims $\frac{2}{5}$ of a mile in total, with each team member responsible for swimming $\frac{2}{15}$ of a mile. The team must complete the swim in $\frac{3}{4}$ of an hour. How many swimmers does Emily need on the relay team?
Solution: To find out how many swimmers Emily needs on the team, divide the total distance ( $\frac{2}{5}$ of a mile) by the distance each team member will swim ( $\frac{2}{15}$ of a mile). $ \dfrac{{\dfrac{2}{5} \text{ mile}}} {{\dfrac{2}{15} \text{ mile per swimmer}}} = {\text{ number of swimmers}} $ Dividing by a fraction is the same as multiplying by the reciprocal. The reciprocal of ${\dfrac{2}{15} \text{ mile per swimmer}}$ is ${\dfrac{15}{2} \text{ swimmers per mile}}$ $ {\dfrac{2}{5}\text{ mile}} \times {\dfrac{15}{2} \text{ swimmers per mile}} = {\text{ number of swimmers}} $ $ \dfrac{{2} \cdot {15}} {{5} \cdot {2}} = {\text{ number of swimmers}} $ Reduce terms with common factors by dividing the $2$ in the numerator and the $2$ in the denominator by $2$ $ \dfrac{{\cancel{2}^{1}} \cdot {15}} {{5} \cdot {\cancel{2}^{1}}} = {\text{ number of swimmers}} $ Reduce terms with common factors by dividing the $15$ in the numerator and the $5$ in the denominator by $5$ $ \dfrac{{1} \cdot {\cancel{15}^{3}}} {{\cancel{5}^{1}} \cdot {1}} = {\text{ number of swimmers}} $ Simplify: $ \dfrac{{1} \cdot {3}} {{1} \cdot {1}} = {3} $ Emily needs 3 swimmers on her team.